Typically, a horizontal-axis wind turbine apparatus comprises a rotor to which one, two or more blades are attached radially from a hub, a nacelle which rotatably supports the rotor by means of supporting a main shaft of the rotor which extends in the horizon and to which the hub is fixed, and a tower that supports the nacelle such that there is a free yaw rotation.
When performing operation in which there is the free yaw rotation of a horizontal axis wind turbine apparatus, a large gyro moment occurs in the rotor (blades, main shaft) or the like when the azimuth angle of the nacelle changes rapidly, which may cause damage to the rotor.
Therefore, it is necessary to suppress rapid change in the azimuth angle of the nacelle. The object of an invention disclosed in Japanese Patent Publication No. 2007-198167 is to absorb the yaw rotation of the nacelle with respect to the tower, and applies a resistance torque to the yaw rotation of the nacelle using a viscous oil type rotary damper or the like.
The object of an invention disclosed in Japanese Patent Publication No. 2006-307653 is to prevent damage by reducing the impact load on a horizontal axis wind turbine that occurs due to sudden yaw movement caused by a strong wind or power failure. In other words, when wind blows having a wind speed that exceeds a specified value, or when a power failure occurs, pivoting is allowed toward the downwind side of the nacelle, however, a brake caliper generates a specified braking force (braking force that is 50% of the maximum braking force) for stabilizing the yaw movement toward the downwind side of the nacelle.
However, in the invention disclosed in Japanese Patent Publication No. 2007-198167, a rotary damper is necessary, which increases the manufacturing cost as well as maintenance and inspection of that damper. Moreover, in the case of a rotary damper, the resistance torque that responds to the input is set according to the damper characteristics, so it is not possible to control the size of the resistance torque for a certain input. The rotary damper is located near the axis of yaw rotation of the nacelle, so it is difficult to obtain large input. Therefore, it is also difficult to obtain large resistance torque.
In the technology disclosed in Japanese Patent Publication 2006-307653, attention must be paid to the wear of the brake, and furthermore, a resistance torque is applied to the yaw movement of the nacelle by a certain amount of friction resistance of the brake. Therefore, there is a possibility that there will be a sudden change in the azimuth angle of the nacelle when the friction resistance exceeds the static friction force, and this technology does not have the characteristic of generating a larger resistance torque for faster changes in the azimuth angle of the nacelle, or that of generating a smaller resistance torque for slower changes in the azimuth angle of the nacelle. Consequently, it is not possible to effectively suppress sudden changes in the azimuth angle of the nacelle, and to effectively lessen and absorb impact or vibration.